1. Field of the Invention
The invention relates to golf club shafts and golf club needs particularly as applied to putters. In particular this invention allows the face of the putter to decrease in loft (moving more to a vertical face) upon impact with the golf ball more efficiently imparting roll to the golf ball.
2. Discussion of Related Art
One of the most important parts of a golfer's game is accurate putting thus minimizing the number of strokes needed to complete a round. For example on a par 4 hole a typical stroke rating is two strokes to reach the green and two putts to get the ball into the hole thus 50% of the strokes that a golfer is rated to take is in putting. Par 5 holes usually rate 3 strokes of driver and fairway play with two putts to get the ball into the hole and par 3 holes rate one T shot and two putting strokes to complete the hole. On average the are an equal number of par 3 and par 5 holes on a golf course with the balance made up of par 4 holes again with the rating versus par 50% of the strokes that a golfer would apply in a round are putts.
Given the importance of accurate putting, great attention has been paid to putter design to accommodate and enhance a golfer's ability to accurately putt. Since there are quite a number of approaches to accurate putting, sanctioning bodies such as the USGA and Royal and Ancient have allowed great latitude in putter design and configuration well beyond that of clubs designed for driving and fairway play. Wide variations club head size and shape, shaft length, and grip size and shape are all within the major sanctioning bodies' rules of putter design.
One issue that has affected putting accuracy is the tendency of the ball to become airborne upon being struck by the face of the putter. The ball becomes airborne (slightly) due primarily to the need to overcome the rotational moment of inertia of the golf ball by applying an axial force at or near the equator of the ball. Since little or no tangential component of force is exerted on the ball, the ball becomes airborne due to frictional resistance between the putting surface and the ball to the applied axial force causing the ball to roil up the face of the putter when struck. While this phenomenon is desirable for fairway play with other clubs it impacts putting accuracy as the ball “skips” in the direction of the axial force as opposed to rolling along the intended line of the putt which is often a curved path since putting greens are not totally flat. This phenomenon of becoming airborne is more prevalent on longer putts where the ball is more firmly struck, imparting a higher axial force and opposite vector frictional force with significant impact on accuracy.
With the flexible connection installed in the shaft, the loft of the putter face, typically a few degrees negative (less than 10 degrees in accordance with USGA rules) from vertical, changes upon impact toward neutral or slightly positive (top of the putter face moves toward the ball). The degree of change in loft is proportional to the force of the strike. This change in loft is analogous to moving a hand from the side of the ball to the top of the ball immediately imparting roll to the ball and not allowing the ball to ride up the face of the putter becoming airborne. In physical terms a tangential, rotational force, is impacted to the ball along with an axial force providing simultaneous translation and rotation to the ball.
While shaft inserts are common in the reference patents cited, shaft inserts such as the reference U.S. Pat. No. 7,500,921 B2 all utilize shaft inserts of varying design to alter stiffness or damping properties without a space between shaft segments. In addition, none of the prior art cited are designed to permit an enhanced loft change in a putter head during the strike of the golf ball.